The synapse is altered by learning and by prolonged exposure to psychoactive drugs.Release of neurotransmitter at the synapse depends on the rates at which synaptic vesicles fuse with the plasma membrane, then recycle and refill. Recently, proteins involved in the fusion step have been identified and shown to form a fusion complex of vesicle and plasma membrane proteins. In addition, an assay has been developed in this lab that screens for the proteins involved in vesicle recycling. The other two proposals also address vesicle refilling. There is evidence that one or more of these three steps in the synaptic cycle are modified by psychoactive drugs. in this proposal assays of fusion complexes and of synaptic vesicle biogenesis will be developed using the neuroendocrine, dopamine-secreting cell line, PC12, since dopamine pathways appear to be central to drug abuse. To determine how the molecules involved in these two steps of the synaptic vesicle cycle are regulated by short-term and long-term modifications, the assays will be used to detect changes in response to secretagogues, NGF, synaptic modulators and selected psychoactive substances.